﻿770 Dr. E. B. Ludlam on the Action of 



keep the surface of the fluorspar perfectly free from a deposit 

 of aluminium given off by the sparks, despite brushing with 

 a camel's-hair brush between each two successive illumi- 

 nations. 



The experiment is very conclusive in its evidence that the 

 presence of chlorine destroys the conductivity produced in 

 air, and that if pure chlorine itself is ionized it can only be 

 so to a minute extent. 



Effect of Moisture. — Carbon disulphide had been introduced 

 into the earlier experiments to act as a conserving agent, but 

 the experiments of Lenard had shown that traces of moisture 

 were likely to act in a similar manner. In this connexion 

 it is of great interest to remember that Baker found that the 

 velocity of combination of hydrogen and chlorine exposed to 

 bright light was very greatly dependent on the presence of a 

 trace of moisture. 



After passing over the usual drying apparatus and through 

 the filter, the air was made to pass over a small surface of 

 water, arranged by calibration to contribute about one gram 

 of water vapour per cubic metre of air. 



The results are tabulated below : — 



Gas. Deflexion cm. 

 + 



Air alone (dry) Tl 1*8 



Air alone (moist) 15*0 15*9 



Air + 10 per cent. Ci 2 (moist)... 0*2 



Cl 2 alone (moist) 



Air again ( „ ) 14*7 15*3 



This table brings out two points very clearly. 



(1) The presence of a trace of water vapour enormously 



increases the action upon air — in the case of the 

 positive ions the increase is more than ten-fold. 



(2) Even this increased effect is completely obliterated 



by chlorine. 



Experiments ivitli the Steam-Jet. 



In ccnclusion it was a matter of interest and some import- 

 ance to ascertain whether chlorine, in the various circum- 

 stances under which it had been examined, gave rise to 

 condensation nuclei or whether it prevented I heir formation. 

 For this purpose the gases on leaving the illumination 

 vessel were made to impinge against an orifice from which 

 a jet of steam was issuing. On sparking for a few seconds 

 the production of a cloud of steam showed instantly whether 

 nuclei were present. 



